1. Field of the Invention
The present invention relates to an electrode structure, and more particularly, to an electrode structure of circuit wiring implemented on a printed circuit board etc.
2. Description of the Related Art
A printed circuit board (PCB) is manufactured by arranging and fixing electronic devices such as semiconductor chips on one or both surfaces of boards made of various synthetic resins, such as phenolic resin insulation plates and epoxy resin insulation plates and implementing circuit wiring for mutual electrical connection between the electronic devices. In recent times, there is an increasing demand for the densification of circuit wiring with the miniaturization of electronic products.
And, in order to meet this demand, as a method of forming circuit wiring, a modified semi-additive process (MSAP) or semi-additive process (SAP) method is widely used.
Looking into a process of forming circuit wiring by an SAP method with reference to the related art document (Korean Patent Publication No. 10-2009-0087149), first, after a seed layer is formed on an insulating layer, a photoresist layer made of a photosensitive material for photolithography, such as a dry film, is coated on the seed layer.
Next, a pattern corresponding to circuit wiring is patterned by performing a developing process after selectively exposing the photoresist layer.
Next, an electroplating process is performed to fill a metal material in the space between the patterns, and the photoresist layer is removed. Finally, circuit wiring of a desired pattern is completed by removing the portion of the seed layer, which is exposed to the outside, through an etching process.
However, in order to obtain a residue-free surface in the etching process, the seed layer is over-etched than the thickness of the seed layer. In this process, undercut that a portion of the bottom of the pattern of the circuit wiring may occur or the width of the pattern of the circuit wiring may be lost.
Therefore, in order to implement a fine circuit, it is preferable that the smaller the thickness of the seed layer is, but since the seed layer is etched by the sulfuric acid (H2SO4) component in the plating solution used in the electroplating process, when the thickness of the seed layer is too small, the electroplating process is not smoothly performed, resulting in the short-circuit between the circuit wiring or the deterioration of signal transmission characteristics of the circuit wiring.
For this reason, a seed layer having at least a predetermined thickness is needed. After all, this acts as an obstacle to the implementation of a fine circuit.